Doing the math is a big part of catering. Knowing the right markups, figuring out how many bottles of wine a table of five needs over the course of an hour, and staffing servers for a party of 100 are all par for the course.
This leads us to the question of how much staff is too much. Messing with staff ratios is probably a bad thing if you're getting charged extra for help that's unnecessary. But it could be very innocent -- maybe your caterer is trying to give his cousin who just got out of jail a leg up (he made some mistakes but is trying to turn his life around). On the other hand, understaffing means fewer servers and cooks but getting the same bill at the end of the evening.